Photocatalytic Oxidation Of Nitrogen Oxides Over G-C₃N₄/{001}TiO₂ Composite Photocatalysts

Photocatalysis is a promising new de-NOx technology. Till now, Ti O2 is still one of the best photocatalyst owing to its cheapness,chemical stability and powerful redox ability. Theoretical and experimental studies show that, in general, thermodynamic instable anatase Ti O2 {001} facets are more reactive than {101} facets which is the generic facets of anatase Ti O2. Numbers of possible applications of {001}Ti O2 were restricted by its narrow spectral response and low quantum efficiency. Unfortunately, it is not easy to dope dopants into the bulk of {001}Ti O2 because its high crystallinity, and it is hard to dope dopants during the growth of Ti O2 sheets without disturbing the formation of anatase Ti O2 {001} facets. Relatively speaking, noble metals surface deposition and semiconductor coupling are more suitable for {001}Ti O2 modification. Considering the above factors, g-C3N4 is chosen to coupling with {001}Ti O2 to expand its spectral response range, improve its quantum efficiency and photocatalytic activity for NOx oxidation.Composite of g-C3N4/{001}Ti O2(Evap-x) was prepared by a facile solvent evaporation method using as-prepared g-C3N4 and {001}Ti O2 as staring materials. The catalysts were characterized by XRD, FT-IR and UV-vis DRS technology. The results shows that {001}Ti O2 still maintained an anatase crystallite structure and a relatively high percentage of {001} facets after calcination for F- remval. All composite samples exhibited higher photocatalytic activity than pure g-C3N4 or {001}Ti O2 nanosheets both under UV and visible linght irradiation. The de-NOx ablity is dependent on the g-C3N4 content, and the optimal content was 10 wt.%.Composite of g-C3N4/{001}Ti O2(CT-x) was prepared through a simple solvent-free strategy using as-prepared F-Ti O2 nanosheets as a starting material. In this strategy, g-C3N4 was in-situ growth on the {001}Ti O2 surface during the calcinations, and F- ion on Ti O2 surface was removed simultaneously. The formation of CT-x composite was confirmed by XRD, FT-IR, XPS, SEM and HRTEM characterization. The spectral response range of all CT-x samples was extended into visible light region, and the tendency was enhanced along with the increasing of g-C3N4 content. All the CT-x composite samples exhibited higher photocatalytic activity than pure g-C3N4 or {001}Ti O2 nanosheets for NOx oxidition, of which, the optimal sample with a g-C3N4 content of 10% exhibited 2.4 and 4.1 times efficiency of pure {001}Ti O2 and g-C3N4 under UV light, and 5.8 times of g-C3N4 under visible light irradiation, respectively. Furthermore, the photocatalytic activity and the photocurrent density of CT-10 was significantly higher than that of Mech-10 and Evap-10,indicating that the compact connected two host phases in composite photocatalyst was available for the separation of photogenerated electorns and holes, resulting in enhaced photocatalytic activity.